During my visit to Iraq last month, it was clear that security is the precondition for political progress and economic development. Until the government and its coalition allies can protect the population, the Iraqi people will increasingly turn to extra-governmental forces, especially Sunni and Shiite militias, for protection. Only when the government has a monopoly on the legitimate use of force will its authority have meaning, and only when its authority has meaning can political activity have the results we seek. The presence of additional coalition forces would allow the Iraqi government to do what it cannot accomplish today on its own -- impose its rule throughout the country. In bringing greater security to Iraq, and chiefly to Baghdad, our forces would give the government a fighting chance to pursue reconciliation.

Contrary to popular notions that U.S. troops are getting "caught in the crossfire" between Sunni and Shiite fighters and are therefore ineffective in suppressing the incipient civil war, the record of U.S. troops in stopping sectarian violence is excellent. Where American soldiers have deployed to areas in turmoil, including Baghdad neighborhoods, the violence has ceased almost immediately. Similarly, the Marines in Anbar province report substantial progress in reducing the nonsectarian, al-Qaeda-based violence that is the predominant cause of instability there.

There are two keys to any increase in U.S. force levels: It must be substantial, and it must be sustained. During my recent trip, commanders there spoke to me of adding as many as five brigades (brigades consist of 3,500 to 5,000 troops) in Baghdad and one or two in Anbar province. This is the minimum we should consider. It would be far better to have too many reinforcements in Iraq than to suffer, once again, the tragic results of insufficient force levels.

The mission of these troops would be to implement the "hold" element, elusive thus far, of the military's "clear, hold, build" strategy: to maintain security in cleared areas, to protect the population and to impose the government's authority. This means establishing local outposts and forging relationships with local leaders, building intelligence networks, safeguarding economic reconstruction activities, overseeing other employment-generating projects and weaning Iraqis off of their reliance on militias for safety. Our troops would work in cooperation with Iraqi forces and stay until the completion of their mission.

The worst of all worlds would be a small, short surge of U.S. forces. We have tried small surges, and they have been ineffective because our commanders lacked the forces necessary to hold territory after it was cleared. Violence, which fell dramatically while U.S. forces were present, spiked as soon as they were gone. Any new surge needs to provide enough American troops to hold the areas on their own.

A short surge would have all the drawbacks associated with greater deployments without giving our troops the time to be effective. Announcing that we are surging for three or six months -- or any other timeline -- would signal to the insurgents and militias that they can wait us out, and it would indicate to the Iraqi public that the enforcement of their government's authority will be fleeting. This would strengthen, not weaken, the power of the militias.

Only by controlling the violence can we pave the way for a political settlement. But once the government wields greater authority it will be incumbent upon Iraqi leaders to take significant steps on their own. These include a commitment to go after the militias, a reconciliation process for insurgents and Baathists, more equitable distribution of government resources, provincial elections that will bring Sunnis into government, and a large increase in employment-generating economic projects.

Increasing U.S. troop levels will expose more brave Americans to danger and increase the number of American casualties. When Congress authorized this war, we were committing America to a mission that entails the greatest sacrifice a country can make, one that falls disproportionately on those Americans who love their country so much that they volunteer to risk their lives to accomplish that mission. And when we authorized this war, we accepted the responsibility to make sure they could prevail. Extending combat tours and accelerating the deployment of additional troops is a terrible sacrifice to impose on the best patriots among us, and they will understandably be disappointed when they are given that order. Then they will shoulder their weapons and do everything they can to protect our country's vital interests in Iraq, and win this war.

There is no guarantee of success in Iraq. We have made many mistakes since 2003, and these will not be easily reversed. But from everything I recently witnessed, I believe that success is still possible. Even greater than the costs incurred thus far and in the future are the catastrophic consequences that would ensue from our failure in Iraq. By surging troops and bringing security to Baghdad and other areas, we will give the Iraqis the best possible chance to succeed. Our national security, and that of our friends and allies, compels us to make our best effort to prevail, and to do it immediately.